The census is a constitutionally mandated count of the population of the U.S., first conducted by the government in 1790 and every ten years since. The count is used for apportioning Congressional seats, as well as many other purposes, such as demographic research, allocating funding, and informing public policy. In the early years, census takers went door-to-door, stopping at every residence to ask questions about the people living there on a particular date. The questions changed a bit each year, at first collecting only very basic information and later adding details such as birth date, the number of children a woman had given birth to, and whether the family had a radio.